Mechanisms for converting reciprocating motion to rotating motion or rotating motion to reciprocating motion have been used for many centuries. For example, from the third century AD Hierapolis Sawmill, in which a water wheel was used to power a horizontal reciprocating saw, to the mechanisms that form the modern internal combustion engine.
The most commonly used mechanism for converting between rotational and reciprocating motion is the crank and slider mechanism. Other known mechanisms include the scotch yoke, swash-plate, wobble plate, and the cam and follower.
The simple crank and slider, scotch yoke, swash plate, and wobble plate mechanisms have a number of disadvantages. In particular, in the conversion between rotational and linear motion, the reciprocating length is set for a given mechanism, and the ratio between the input and output is fixed at 1:1 reciprocation to rotation.
In addition, crank and slider mechanisms produce un-balanced motions and require counter-balancing weights to reduce the effects of that un-balanced motion. Scotch yoke mechanisms need larger amounts of material around the yoke for adequate strength. Depending on the application and type of design, some wobble and swash plate parts are prone to fatigue failure and excessive wear. Swash plates that overcome these reliability issues are typically expensive to manufacture. The applications for wobble plates and swash plates are limited due to their high point loading.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents or such sources of information is not to be construed as an admission that such documents or such sources of information, in any jurisdiction, are prior art or form part of the common general knowledge in the art.
It is an object of at least preferred embodiments of the present invention to provide a mechanism that addresses or one or more of the above disadvantages and/or that least provides the public with a useful alternative.